Astronomer, educator, and science communicator Ethan Siegel has a new book, Beyond the Galaxy: How Humanity Looked Beyond the Milky Way and Discovered the Entire Universe. I know Ethan a bit, both from interacting with him on Twitter and from meeting him at the 2015 AAS meeting, and he’s a very intersting person. So I figured that the book, which attempts to cover extragalactic astronomy and cosmology in a less textbook-y way than the many Astronomy 101 textbooks already on the market, would also be interesting. I wrote about teaching a one-term cosmology class using The State of the Universe by P.G. Ferreira as the text here; I wasn’t totally happy with using that book, so I was looking at Siegel’s book as a possible text should I teach that course again.

Siegel states in his introduction that he wants to tell the story of how we know what we know about the universe. This is a laudable goal, although in my experience it’s been something of a tough sell with non-science students. (Maybe I’m just not doing it right, or maybe it’s just difficult for scientists to see why someone wouldn’t be interested in the methods as well as the conclusions!)

I bought the e-book directly from the publisher. Somewhat unsually, the format consists of separate PDF files for each chapter; it’s kind of a pain to download these one at a time but it does make the file size more manageable. The book format is one column of black-and-white text, with colour figures (images and line drawings, at least a dozen per chapter). Siegel himself made many of the figures, while others come from acknowledged public sources. Most are not super-fancy, which I expect helped to keep the cost down. There are no textbook-like features such as call-out boxes, exercises, or glossaries. In my opinion the text requires a greater reading fluency than the typical introductory college textbook, although I don’t think it’s harder going than a magazine like New Scientist or Wired. Siegel’s style is conversational and easy to follow.

Chapter 1 of the book explains what humans knew about the universe beyond Earth at the start of the 20th century. It covers the material that would usually take up the first few weeks or even months of an introductory astronomy course: the celestial sphere, moon phases and eclipses, the geocentric and heliocentric models, parallax, early use of telescopes, and the beginnings of modern physics (radioactivity, special relativity). This is a lot of material to pack into 47 pages, and I suspect that a typical student wanting to master all of of might need additional resources. Some topics are skimmed pretty quickly: for example, the description of the Michelson-Morley experiment mentions (interference) fringes several times without explain what the word means in this context. In terms of setting the stage for what follows, I think it has close to the right level of detail.

The remaining chapters — a total of 10 over 360 pages, plus a shorter summary chapter — cover pretty much everything that’s in the scientific story of the universe: relativity, the nature of galaxies, the expanding universe, the cosmic microwave background, the big bang, nucleosynthesis (primordial and stellar), inflation, particle physics and antimatter, dark matter and dark energy. As in chapter 1, there is lots of material here. There are pieces of jargon that aren’t terribly well-explained (baryon acoustic oscillations, blue stragglers) and which I wouldn’t try to cover in an introductory course. There are also some real gems of explanation: I think I might possibly understand CP violation and inflationary potentials well enough to explain them now!

Because the book contains such a wealth of material, I wonder if it would be difficult for a student to pick out the most important ideas. One aspect of the book that helps with this is repetition: a number of ideas make appearances in more than one chapter, and several diagrams appear multiple times in different versions. The summary chapter also helps put the big picture back together; possibly a “here’s where we’re going” roadmap in the preface would have helped as well.

So would I use this book as a textbook for the one-semester introduction to cosmology course we teach here? Lots of factors go into such a decision, but I’d certainly consider it very seriously. Beyond the Galaxy is up-to-date, engaging, and written by someone who clearly has a lot of experience explaining cosmological topics to the non-specialist. I’d recommend it for the interested member of the public who wants to go beyond the one-hour public lecture by a scientist or a 30-second news story: this book delivers on its promise to give the whole story of modern cosmology.